How Are Stem Cells Obtained? Sources and Methods

Stem cells are obtained from a surprisingly wide range of sources, from early-stage embryos and adult bone marrow to reprogrammed skin cells and umbilical cord tissue. The method used depends on the type of stem cell needed and the intended application. Some approaches require surgical procedures or blood draws; others are performed entirely in the lab using cells already collected. Understanding where stem cells come from and how they are isolated clears up a lot of confusion about what is actually happening in both routine medical treatments and cutting-edge research.

Embryonic Stem Cells

Embryonic stem cells (ESCs) are derived from the inner cell mass of early-stage embryos, typically at the blastocyst stage, roughly five to six days after fertilization.¹ In practice, these embryos come from in vitro fertilization clinics, where couples may donate surplus embryos they no longer plan to use for reproduction. The embryos are never taken from a pregnancy.

Getting the inner cell mass out of a blastocyst is delicate work. The most established technique, called immunosurgery, uses antibodies and complement proteins to destroy the outer layer of cells (the trophoblast) while leaving the inner cell mass intact. However, this only works well with high-quality blastocysts whose outer layer is structurally complete, since any gaps would expose the inner cells to damage too.² Newer approaches avoid the cytotoxic chemicals altogether. Microsurgical methods use fine needles under a microscope to physically peel the outer cell layer away from the inner cell mass, which has shown higher success rates in establishing stem cell lines.³ Laser-assisted techniques have also been developed to cut through the protective shell around the embryo and ablate the trophoblast without exposing the inner cells to antibodies.²

Once isolated, the inner cell mass is placed onto a culture surface where the cells can attach, divide, and eventually form a stable embryonic stem cell line. These cells are pluripotent, meaning they can become virtually any cell type in the body, which is what makes them so valuable for research and medicine.

Adult Stem Cells from Bone Marrow and Fat

Adult stem cells are found in many tissues throughout the body, where they serve as a repair system. Two of the most commonly harvested sources are bone marrow and adipose (fat) tissue.

Bone marrow aspiration involves inserting a needle into the back of the hip bone and drawing out a small volume of marrow. It is typically done under local anesthesia and takes about half an hour. The collected marrow contains a mixed population of blood-forming stem cells and mesenchymal stem cells, which can develop into bone, cartilage, and fat cells. Bone marrow transplants have been a standard treatment for blood cancers and certain immune disorders for decades.

Adipose tissue harvested during liposuction or minor surgical procedures is an increasingly popular alternative. A key practical difference is yield: a harvest of fat tissue under local anesthesia provides roughly 40 times more mesenchymal stem cells than a comparable bone marrow harvest.⁴ The isolation process for fat-derived cells is straightforward: the harvested tissue is enzymatically digested, filtered, and centrifuged to separate the stem cells from fat cells and other material. Donor-matched comparisons have confirmed that stem cells from both sources share surface markers and similar characteristics, though research continues into whether one behaves better than the other for specific applications.⁵

Mobilized Peripheral Blood

You do not always need to go directly into the bone marrow. Mobilized peripheral blood has become the predominant source of stem cells for blood-forming transplants.⁶ The idea is to coax stem cells out of the bone marrow and into the bloodstream, where they can be collected much less invasively.

This is done by giving the patient or donor injections of a growth factor called G-CSF over several days. G-CSF stimulates the bone marrow to produce and release large numbers of stem cells into circulating blood. Once levels are high enough, the blood is drawn through an apheresis machine, which separates out the stem cells and returns the rest of the blood to the person. In a recent study of multiple myeloma patients, all 176 patients achieved successful mobilization with G-CSF, and the median collection took just two days of apheresis.⁷ For the small percentage of patients whose cells do not mobilize well with G-CSF alone, a drug called plerixafor can be added to boost the release.

This approach works in children too. A study of 64 mobilization and apheresis procedures in pediatric cancer patients, some weighing as little as 15 kilograms, achieved a 98% success rate in collecting enough stem cells for transplant.⁸

Umbilical Cord Blood and Tissue

Birth provides a one-time opportunity to collect stem cells that would otherwise be discarded. Cord blood, the blood remaining in the umbilical cord and placenta after delivery, is rich in blood-forming stem cells and has been used in transplants since the late 1980s. Collection is painless and poses no risk to mother or baby: the blood is simply drained from the clamped cord into a collection bag after the baby is delivered.

The cord tissue itself, specifically a gelatinous substance called Wharton’s jelly that cushions the blood vessels inside the umbilical cord, is another source of mesenchymal stem cells.⁹ These cells are isolated by either enzymatic digestion of the jelly or an explant method, where small pieces of tissue are placed in culture dishes and the stem cells migrate out on their own. The explant approach is simpler and cheaper.¹⁰ For cord blood, a density gradient centrifugation method using a substance called Ficoll-Paque separates the stem cells from other blood components while eliminating unwanted cell types.¹⁰

Private cord blood banks market their services to expectant parents, but the chance that a child will actually need their own banked cord blood is very small. Public cord blood banks, where donations are made available to anyone who needs a match, are generally considered a more practical use of this resource.

Induced Pluripotent Stem Cells

In 2006, Shinya Yamanaka’s lab demonstrated something that reshaped the field: ordinary mouse skin cells could be reprogrammed into cells that behave like embryonic stem cells by introducing just four genes.¹¹ The following year, the same approach worked with adult human skin cells.¹² These induced pluripotent stem cells, or iPSCs, looked and acted like embryonic stem cells: they could self-renew, expressed the same marker genes, and could differentiate into cell types from all three fundamental tissue layers.

The original method used viruses to deliver the reprogramming genes into the cells’ DNA. That worked, but inserting foreign DNA permanently into the genome carries risks, including the possibility of activating cancer-related genes. Cells reprogrammed this way show substantially more genetic disruption: one comparison found that the largest genomic copy-number variations in virus-reprogrammed cell lines were about 20 times larger than in cell lines made with non-integrating methods.¹³

That finding pushed the field toward non-integrating approaches. Episomal plasmids, which deliver genes temporarily without stitching them into the chromosome, are now widely used. One group showed that a single transfection of blood cells with an improved episomal plasmid carrying five reprogramming factors could generate up to 1,000 iPSC colonies from just two million starting cells within 14 days.¹⁴ The fact that blood cells work as starting material is a practical advantage: a simple blood draw replaces the need for a skin biopsy. Chemical compounds combined with episomal vectors have also enabled iPSC creation from fibroblasts of multiple species, including dogs and pigs.¹⁵

Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer, the technique behind Dolly the sheep, has a stem cell application too. The nucleus from an adult cell is inserted into an egg cell whose own nucleus has been removed. Under the right conditions, the egg begins dividing as if it were a fertilized embryo, and a blastocyst can form from which embryonic stem cells are derived. This produces patient-matched stem cells without needing a fertilized embryo in the traditional sense.¹⁶

Proof of concept in primates came when researchers used skin cells from an adult rhesus macaque to create blastocysts and successfully established two embryonic stem cell lines from them.¹⁷ The technique remains technically demanding and requires donor egg cells, which limits its widespread use. With the rise of iPSC technology, which achieves similar patient-matching goals more simply, SCNT has moved somewhat to the margins of the field, though it still offers insights into how reprogramming works at a fundamental level.

Transdifferentiation

A more recent concept bypasses the pluripotent stage entirely. In transdifferentiation, or direct reprogramming, one mature cell type is converted into another without first being turned back into a stem cell.¹⁸ Researchers have converted skin cells directly into neurons, heart muscle cells, and other types by delivering specific combinations of transcription factors.

The appeal is efficiency and safety. Skipping the pluripotent state could reduce the risk of tumor formation that comes with undifferentiated stem cells, and could shorten the timeline from cell collection to therapeutic use.¹⁹ Transdifferentiation is still largely experimental, but it represents an intriguing alternative to the standard stem-cell pipeline for certain applications.

Sorting and Purifying Stem Cells

Regardless of the source, harvested tissue almost never contains pure stem cells. It is a mixture, and the stem cells need to be separated from everything else. Two main technologies handle this.

Fluorescence-activated cell sorting (FACS) labels cells with fluorescent antibodies that bind to specific surface proteins. The cells are then streamed past a laser one at a time, and the machine sorts them into collection tubes based on which markers they carry. Magnetic-activated cell sorting (MACS) uses antibody-coated magnetic beads instead: cells with the target marker stick to the beads and are pulled out of the mixture by a magnet. Both methods achieve high purity and keep the cells alive.²⁰

What makes this step powerful is the ability to isolate specific subsets. Bone marrow mesenchymal stem cells, for instance, can be enriched up to 180-fold by targeting certain surface marker combinations.²¹ Researchers working with embryonic stem cell-derived neural cells have developed detailed marker profiles that let them sort out immature stem cells, neural precursors, and mature neurons from the same culture dish.²²

Culturing and Expanding Stem Cells

Once isolated, stem cells need to be grown in culture, and doing this well is harder than it sounds. Stem cells are fussy. The surface they grow on, the nutrients in their medium, and even the density at which they are plated all affect whether they stay as stem cells or start differentiating into something else.

Early culture methods relied on “feeder layers,” beds of inactivated mouse cells that provided signals to keep human stem cells in their undifferentiated state. The obvious downside is contamination risk from animal material. The field has since moved toward defined, feeder-free systems. Laminin proteins, particularly laminin-521, have emerged as effective culture surfaces for maintaining human pluripotent stem cells without feeder cells.²³ A combination of laminin-521 and E-cadherin achieved roughly 20% clonal survival of individual embryonic stem cells, something that was previously very difficult to accomplish.²³ Eliminating animal-derived components from the whole system is a priority for any stem cells headed toward clinical use.

Scaling Up for Clinical and Commercial Use

Growing enough stem cells for a single patient is one thing. Manufacturing them by the billions for off-the-shelf therapies is a different engineering challenge entirely. Standard flat culture dishes run out of surface area quickly, and stacking more dishes is not a real solution when you need industrial quantities.

Bioreactors paired with microcarriers have become the leading approach. Microcarriers are tiny beads, often made from degradable materials like gelatin, that give cells a three-dimensional surface to grow on while suspended in stirred culture medium. Using vertical wheel bioreactors, researchers have achieved 9- to 16-fold expansion of mesenchymal stem cells over eight days on degradable microcarriers, with the added benefit that the beads dissolve during harvest so you do not have to scrape cells off.²⁴ This platform has been demonstrated at volumes up to three liters, a meaningful step toward clinical-scale production.²⁵ Work on serum-free medium formulations is progressing in parallel, further reducing reliance on animal products.²⁶

Cryopreservation and Banking

Stem cells are only useful if they can be stored reliably. Cryopreservation, freezing cells to extremely low temperatures, is the standard method for long-term storage. Cells are typically suspended in a cryoprotective solution containing dimethyl sulfoxide (DMSO), which prevents ice crystals from forming inside cells and rupturing them. They are then cooled at a controlled rate and stored in liquid nitrogen at around minus 196°C or in the vapor phase just above it.²⁷

Cord blood banking is the most familiar consumer-facing application of stem cell cryopreservation. Both cord blood and cord tissue can be banked, with separate protocols for each.²⁸ Efforts are ongoing to standardize processing, quality control, and storage methods across institutions, which remains a significant hurdle for building coordinated global biobanking networks.²⁹ The methodology matters: cells frozen using inconsistent protocols may have lower viability when thawed years later, which directly affects transplant outcomes.

Safety Concerns and Genomic Monitoring

Every time stem cells divide in culture, there is a chance they pick up genetic changes. Most of these are harmless, but some can push cells toward uncontrolled growth. This is especially relevant for pluripotent stem cells (both embryonic and induced), which are expanded extensively before use. Human pluripotent stem cells are known to acquire genomic alterations during culture, and while there is not yet strong evidence directly linking these changes to malignancy in transplanted cells, the theoretical risk is taken seriously.³⁰

Research on iPSC lines has found a plausible relationship between the number of copy-number variation sites in a cell line’s genome and its tendency to form tumors when tested in animal models.³¹ The practical recommendation from the field is clear: any cells intended for transplant should be monitored throughout their preparation using high-resolution genomic screening to catch problematic changes before they reach a patient.³⁰

Ethics and Regulation of Embryonic Sources

Embryonic stem cell research remains ethically contentious because it involves the destruction of a human embryo. In the United States, NIH guidelines established in 2009 require that embryonic stem cell lines used in federally funded research be derived from embryos donated from IVF clinics, with documented informed consent from the donors and no financial inducements.³² Many countries have their own regulations, ranging from permissive (the United Kingdom, where embryo creation for research is allowed under license) to outright bans.

The development of iPSC technology was partly motivated by these ethical constraints, since reprogramming adult cells avoids embryo destruction entirely. However, iPSCs bring their own regulatory challenges around genomic stability and manufacturing standards. Adult stem cell therapies from bone marrow and adipose tissue face a different regulatory landscape: they are often considered minimally manipulated and can be used under less restrictive frameworks, though this has also opened the door to unproven commercial “stem cell clinics” that sell treatments with little evidence behind them. Regulatory agencies have been working to distinguish legitimate cell therapies from those that are marketed prematurely.

Less Common and Emerging Sources

Beyond the major sources, researchers have isolated stem cells from a variety of other tissues. The olfactory mucosa, the tissue lining the nasal cavity, harbors a population of stem cells that can be biopsied from living patients using relatively simple procedures.³³ Dental pulp, the soft tissue inside teeth, contains mesenchymal stem cells that are sometimes collected from extracted wisdom teeth. These niche sources are mostly in the research phase but illustrate how broadly stem cells are distributed throughout the body.

Another growing area involves using adult stem cells from tissue biopsies to grow organoids, miniature three-dimensional structures that mimic the architecture of actual organs. Human intestinal organoids, for example, can be established from small intestine or colon biopsies, providing a personalized model of a patient’s gut tissue for drug testing or disease study.³⁴ Veterinary medicine is also adopting stem cell therapies, with mesenchymal stem cells being the most widely used type in animals due to their straightforward isolation and the absence of the ethical concerns that surround embryonic cells.³⁵